1 Overview
Loss-in-weight feeder is a kind of quantitative weighing feeding device. For the purpose of use, the weightless scale is used for dynamic continuous weighing process, which can weigh and quantitatively control the materials that need continuous feeding. There are also material instantaneous flow and cumulative flow display. In principle, it is a static weighing device that uses the weighing technology of a static silo scale, and weighs the silo with a load cell. However, in the controller of the weightless scale, the weight calculation lost by the silo scale per unit time is obtained to obtain the instantaneous flow rate of the material.
Figure 1 is a schematic diagram of the working principle of the weightless scale.
Figure 1 Schematic diagram of the working principle of the weightless scale
Figure 1 is a schematic diagram of the structure of a weightless scale. When the weighing bin is empty, the filling valve can be opened. When the maximum level is reached, the charging valve is closed, and the weighing bin is replaced by a weightless scale. Support. In order to make the weighing accurate, the upper and lower parts of the weighing bin are connected by a flexible inlet or outlet so that the weight of the front and rear equipment and the materials therein are not added to the weighing bin.
The right side of Figure 1 is a schematic diagram of the continuous feeding process, and the continuous feeding process has numerous cycles (three cycles are illustrated in the figure). Each cycle consists of 2 cycles: when the weighing bin is empty, the charging valve is opened, and the weight of the weighing bin is continuously increased. When the maximum level is reached at time t1, the charging valve is closed. The screw conveyor starts to unload, at which time the weight loss scale starts to work; after a period of time, when the weight of the weighing silo material decreases continuously and reaches the minimum level at time t2, the charging valve reopens, and the time t1~t2 is Gravity feeding cycle; after a period of time, when the weight of the weighing silo increases continuously and reaches the highest level again at time t3, the charging valve closes, and the period from t2 to t3 is the reloading cycle, so it is repeated .
In the gravity feed cycle, the screw conveyor speed is controlled according to the instantaneous flow rate to achieve stable feeding; during the refilling cycle, the screw conveyor speed is maintained at the same speed as before the start of the cycle, and is fed in constant volume flow control mode. .
Because the weightless scale combines dynamic weighing and static weighing, it combines intermittent feeding and continuous discharging, and the structure is easy to seal. It is suitable for weighing and batching control of fine materials such as cement, lime powder, coal powder, food, and pharmaceuticals. High weighing accuracy and control accuracy can be achieved.
The importance of the design of the operating parameters of the weightless scale
When designing the weightless scale, it is necessary to consider the operating parameters such as the loading frequency, the reloading volume, the weighing bin volume, and the reloading speed. Otherwise, the weightless scale cannot work normally.
For example, when ordering a weightless scale from a user's field equipment, the manufacturer only purchases 100 kg load cells at the time of ordering. After being put into operation, it is found that the zero point is unstable, and the flow sometimes has no display and other faults. After the manufacturer sent people to the scene, they learned that the user's material is boric acid, the density is 1510kg/m3, the maximum flow rate is only 36kg/h, and the common flow rate is 21~24kg/h. The flow rate is so small, the silo is supported by three 100kg load cells, and the analysis silo has a large capacity, which is an unreasonable selection problem. Another problem is that the silo is connected to the equipment with vibration source during installation.
We can calculate according to the rule of thumb recommended in the article, “Refilling frequency is 15 to 20 times/h at the maximum feeding amountâ€, and the weight of each reloading is 36/15~36/20, ie 1.8kg~2.4kg, the weight of each load cell is less than 1kg, and the effective range is about 0.5~1%. Generally, the effective range of the load cell should be at least 10~30% or more to ensure a more accurate weighing. According to the weight of the material 2.4kg plus the weight of the silo and discharge equipment (such as screw conveyor), the total weight is about 10kg. If using 3 load cells, the range of each load cell can be 5kg~10kg. . That is, the 100kg sensor range originally ordered is 10-20 times larger, which results in poor stability of the weightless scale and low weighing accuracy.
This example shows that the design of the weightless scale also needs to follow the design rules, and the equipment and operating parameters of the weightless scale cannot be determined without calculation.
Design calculation of operating parameters of 3 weight loss scale
3.1 Loading frequency calculation
Figure 1 shows how the loading frequency is appropriate for each cycle of the weight loss scale.
For weightless scales, the greater the proportion of gravity feed cycle time (time ratio = gravity feed cycle time / reload cycle time) in each cycle, the better, usually should be greater than 10:1. This is because the accuracy of the gravity feed cycle is much higher than the reload cycle, and the greater the proportion of the gravity feed cycle time, the higher the overall accuracy of the weight loss scale.
The number of cycles per unit time of the weightless scale is usually expressed as the number of cycles per hour at the maximum feed rate, ie, /h. Since the premise is based on the maximum dosing amount per hour, the dosing amount per unit time (for example, per second) is a fixed value. The fewer the number of cycles, the more the amount of charge per load, the larger the volume and weight of the weighing bin, and the lower the accuracy of the weight loss calculation using a large range of load cells; the more cycles, the more The less the amount of material, the smaller the volume and weight of the weighing bin, and the higher the accuracy of the weight loss calculation using a small-range weighing cell. However, the number of cycles is too high, and the loading and unloading equipment frequently starts and stops. It is not good for the controller of the weightless scale to frequently switch between the gravity feeding cycle and the reloading cycle.
The recommended reloading frequency is shown in Table 1, but the three recommended charging frequencies are the main recommendations.
Table 1 Recommended reload frequency
| Reloading frequency at maximum feed rate, times / h | Each cycle time, Min |
| 6 | 10 |
| 10 | 6 |
| 15 | 4 |
| 20 | 3 |
| 30 | 2 |
As a rule of thumb, most of the loss-in-weight feeding systems, especially for powdered materials and poorly flowable pellets, have a refilling frequency of 15 to 20 times per hour at the maximum feed rate. When the feeding amount is less than the maximum feeding amount, the reloading frequency is reduced, so that the proportion of the gravity feeding cycle time is larger, which is more favorable for improving the precision.
As an exception to the rule of thumb, some applications with particularly low feed flow rates, although the silo volume is very small, can still store materials for one hour or longer and refill for more than 1 h. The following example:
Maximum feed flow rate 2kg/h
Material pile weight 803kg/m3
Maximum volume feed flow 2/803=0.0025m3/h
If the silo volume is 0.01m3 (generally equivalent to the size of a cubic silo such as 250mm × 250mm × 250mm), the amount of material is sufficient for 2h~3h, and the amount of each feed is below 10kg, so no automatic loading is required. The tooling can meet the production requirements, but its flow control accuracy is slightly lower.
3.2 Reloading volume calculation
With the reload frequency selected, the refill volume and total feed volume can be calculated. Take a weight loss scale as an example:
Maximum feed flow rate 270kg/h
Material bulk density 480kg/m3
Maximum volume feed flow 270/480 = 0.562m3/h
At the maximum feed rate, the frequency of refilling is chosen to be 15 times/h.
Reload volume calculation formula:
Reloading volume = maximum feeding amount (kg / h) ÷ capacity (kg / m3) ÷ reloading frequency (reloading times / h)
In this example, the reload volume = 270 ÷ 480 ÷ 15 = 0.0375 m3
3.3 Weighing silo volume calculation
The designed weighing silo volume must be greater than the calculated reloading volume, because it is considered that there will inevitably be some “residual material†and the top of the silo may not be filled when the reloading begins. The "free space", if each accounted for 20%, the reloading volume is divided by 0.6, the required silo volume can be obtained, and the final weighing silo capacity should also be based on the shaped silo capacity. whole.
Reload volume calculation formula:
Weighing silo volume = reloading volume ÷k
Where: k is the calculation of the residual capacity of the silo, which can be taken as 0.4~0.7, and 0.6 is recommended.
In this example, the weighing bin volume = 0.0375 ÷ 0.6 = 0.0625 m3
If the capacity of the shaped silo is 0.6 m3, 0.8 m3, 1.0 m3, etc., it should be rounded up to 0.08 m3, and the weighing bin volume should be 0.08 m3.
3.4 Reloading speed calculation
Since the weight-loss scale adopts a low-precision constant-volume feeding method in the re-loading cycle, the feeder is required to reload quickly (generally should be controlled in 5s~20s).
Reloading speed calculation formula:
Reloading speed = [reloading volume (m3) ÷ reloading time (s) × 60 (s / min)] + [maximum volumetric feed flow (m3 / h) ÷ 60 (min / h)]
The reloading speed in Equation 2 consists of two items. The first item is the required loading speed according to the reloading volume, and the second item is often ignored by many people. It indicates the unloading speed at the same time of loading. It needs to replenish this part of the material when reloading.
In this case,
Reloading volume: 0.0375m3
Reload time selected as: 8s
Maximum volume feed flow: 0.562m3/h
Then: reloading speed = (0.0375 ÷ 8 × 60) + (0.562 ÷ 60) = 0.281 + 0.009 = 0.289 m3 / min
The reloading speed can also be calculated directly from the maximum feed rate based on past experience:
Maximum volume feed flow: 270/0.48=0.562m3/h
The reloading speed is converted into the hourly flow rate: 0.289×60=17.34m3/h
Reloading speed = 17.34 / 0.562 = 30.85
The calculation results show that the reloading speed is approximately equal to 30 times the maximum feeding speed. That is to say, the calculation result can be referred to, and the calculation of the reloading speed of other weightless scales is calculated by 25 to 40 times the maximum feeding speed. .
4 several application examples
4.1 German food company weightless scale
Bel Foods produces a variety of food ingredients and ingredients for baked goods, confectionery, dairy products and more. In the production process, it is essential to provide accurate and continuous flour ingredients. The dosage is 1t/h~4t/h, the weighing container capacity is 200kg material, and the refilling is performed every 3min~12min (loading frequency is 5). ~20 times / h).
4.2 Ma Steel New District Sintering Machine Weight Loss Scale
Magang New District 2×360m3 sintering machine quicklime weight loss scale, feeding flow 20t/h~50t/h, using 3 sets of 2.5t load cell support, reloading every 5min~10min (loading frequency is 6~12 times) /h). According to the data analysis of the maximum feed flow rate and refilling interval, the weight of each reloading is about 400kg, and the silo capacity is about 1t~2t.
5 Conclusion
As a new type of quantitative weighing and feeding equipment, weightless scales have been used more and more in the food, pharmaceutical, chemical, metallurgical and other industries in recent years, but there are few data introductions on how to determine the operating parameters when designing and selecting. The author combines foreign materials with domestic application experience and lists a complete calculation example that can be used by manufacturers and users to design weightless scales.
Aurora Disposable Vape Device Vaping Pod Systems
Shenzhen WeiKa Technology Co.,Ltd. is a professional e-cigarette manufacturer and enterprise integrating R&D, design, production and sales and service of the electronic cigarette atomizer products, established in 2020.
We are actively developing and producing all kinds of reliable and unique atomizer products. We centre on research, developing, high quality and safety, and focus on better vaping experience in all aspects to our customers. We have advanced production equipment and strict production control system, each process has strict management, from production to delivery have been strictly tested to ensure the classic quality. Zgarvape for the future!
Aurora E-cigarette Cartridge is loved by the majority of consumers for its gorgeous and changeable colors, especially at night or in the dark. Fruits Flavors series, plant flavors series & special flavors series.Up to 16 different flavors for choices. A new design of gradient our disposable vape is impressive. Our vape pen and pods are matched with all the brands on the market. You can use other brand's vape pen with our vape pods. Aurora series Pods systems, the first choice for professional users!
16 Available Flavors (3Pods*2ml):
Amazing Cantaloupe / Coke on the Rocks / Ice Coconut / Ice Lolly / Iced Mung Bean / Longjing Tea / Mango Feast / Mountain Spring / Peach Tempting / Pineapple Juice / Refreshing Melon / Refreshing Mint / Rich Strawberry / Rose Litchi / The Ocean / Watermelon Juice
Aurora Pods 1.0,Pod System Vape,Pos Systems Touch Screen,Empty Disposable Vape Pod System,400Puffs Pod Vape System
ZGAR INTERNATIONAL(HK)CO., LIMITED , https://www.zgarvapor.com